1. Field of the Invention
The present invention relates to a lining material for pipe lines, chiefly those buried in the ground, such as sewage pipes, which lining material is capable of forming a rigid inner pipe for repair and/or reinforcement, and to a process for providing the pipe line with such rigid inner pipe for repair and/or reinforcement. More particularly, the present invention relates to a lining material for pipe lines already constructed and buried in the ground, for the purpose of repair and/or reinforcement, and to a process for providing the pipe lines with a fiber-reinforced or a fabric-fiber-reinforced plastic lining. The process comprises inserting into the pipe lines a lining material including a sheet impregnated with a thermohardenable resin, which sheet is somewhat overlapped in both lateral end portions slidably to form a tubular sheet, inflating the lining material by introducing a pressurized fluid thereinto and internally heating the lining material to form an integrally solidified rigid inner pipe within the pipe line.
2. Description of the Prior Art
It is well known that pipe lines, irrespective of whether they are constructed on the ground or in the ground, can be lined with a fiber-reinforced plastic material for the purpose of reinforcement and/or repair. Pipe lines buried in the ground cannot easily be decomposed for lining, or be inspected for damage. Accordingly, special arts and materials are needed for lining pipe lines buried in the ground, such as gas pipe lines, city water pipe lines and sewage pipe lines. In the past, various lining materials have been proposed for repair and/or reinforcement of such underground pipe lines. In recent years, a tubular mat of a strong fibrous material impregnated with a liquid thermohardenable resin, which is overlapped in both lateral end portions so as to be slidable and interposed between an inner tube and an outer film and is then heated to thicken the resin, has been proposed as a pipe-lining material. This mat itself is called "Sheet Molding Compound" (referred to hereinafter as SMC) by ASTM. This SMC lining material ls manufactured, for example, by spreading a strong fibrous material such as glass fiber over a plastic film capable of easily splitting off, to form a fibrous mat, impregnating the fibrous mat on the film with a thermohardenable resin such as styrene or an unsaturated polyester, overlaying the mat with a tubular film and heating the mat under a controlled condition to thicken the resin by effecting partial polymerization of the resin. In this case, the resin-impregnated mat on the tubular film is overlapped in both its lateral end portions so as to be slidable in both directions to form a tubular mat. The two films on both sides of the resin-impregnated mat serve to prevent evaporation of the thermohardenable resin in the mat but the outer film is split off prior to being inserted into pipe lines.
This lining material containing SMC the main component affords, after curing, a rigid fiber-reinforced plastic (FRP) lining on the inner surface of pipe lines, thereby attaining the purpose of reinforcement and/or repair of the pipe lines. However, this lining material has the drawback that when it is inserted into pipe lines, especially long or curved ones, an extremely strong force is exerted to SMC due to frictional resistance against the inner surface of the pipe lines so that the SMC is locally stretched to reduce its thickness or suffers from various damage, and in the extreme case, breaks down in the location where damage become serious. As the SMC lining material has a number of disadvantages to be overcome in addition to the above mentioned, a new type lining material was proposed in Japanese Patent Appln. No. Hei 2-95880 (referred to hereinafter as Ref. 1) . Disclosed in Ref. 1 is a newest lining material now currently used which comprises in place of the mat of SMC a sheet comprised of a fabric and a mat of fibers of high tenacity impregnated with a thickened liquid thermohardenable resin to form a fabric-fiber-reinforced composite molding sheet (referred to hereinafter simply as FCM-sheet). This FCM-sheet is also coated on both sides with two plastic films, one of which constitutes an outermost layer capable of easily splitting off before insertion of the lining material into pipe lines. Stretchability of SMC by strong tension, which is one of the great disadvantages of SMC, is overcome to a certain degree by FCM-sheet since a fabric in addition to fibers is impregnated with a thermohardenable resin, unlike SMC wherein fibers alone are impregnated with the resin so that the resultant sheet is resistant to biaxial tension. However, both SMC and FCM-sheet lining materials are similar in appearance since they are made up by overlapping both lateral end portions of the sheet material with each other to form a tubular material in such manner that the overlapped portions of the tubular material are somewhat slidable in circumferentially opposite directions in compliance with the diameter of the pipe lines. In order to facilitate insertion of the lining material into a pipe line, the diameter of the tubular sheet, the lateral end portions of which are overlapped with each other, is normally smaller than the inner diameter of the pipe line. However, the lining material once inserted into the pipe line is inflated to bring it into contact with the pipe line prior to curing.
Among underground pipe lines, a sewage pipe line is usually made of a porcelain pipe or a Hume concrete pipe and thus is brittle and easily broken by earthquake or any vicinal underground work accompanying vibration. Otherwise, sewage pipe lines, if superannuated, become so brittle that they often undergo local breakage or rupture or are damaged so as to be ready to fall into pieces. When such brittle sewage pipe lines are lined with either of the SMC or FCM-sheet lining material for reinforcement, the lining material in the form of a tube formed by overlapping both lateral end portions of the sheet so as to be slidable in circumferential direction is inserted into such pipe lines and the tubular lining material is then inflated internally by fluid pressure whereby the overlapped lateral end portions are slid in compliance with the inner diameter, i.e. the inner circumferential length of the pipe lines. If the pipe lines have a locally broken portion, the lining material is expanded out of the broken portion by internal pressure whereby the overlapped lateral end portions of the lining material are excessively slid to form a cleavage. If the pipe lines are considerably superannuated as a whole, they will be ruptured over a significant length for the reason that they are pressed internally by the expanding lining material and fall into pieces locally. In this case, sliding of the overlapped lateral end portions of the lining material goes too far so that the opening may be formed between the lateral end portions of the lining material over a significant length. Although FCM-sheet can suppress stretchability of SMC by tension, this phenomenon commonly occurs irrespective of whether the lining material is SMC or FCM-sheet as both materials wherein the lateral end portions are weakly bonded merely by the thickened liquid resin are less resistant to internal expansion by fluid pressure.
This drawback in case of using the SMC or FCM-sheet lining material can be exaggeratedly shown in the accompanying FIG. 1 wherein a lining material is inserted into a pipe line, especially a sewage pipe, having a broken portion and is inflated internally by fluid pressure. A pipe line 101 has a broken portion 102 where the lining material 103 made of SMC or FCM-sheet is spread out by fluid pressure. For exaggeration's sake, the overlapped lateral end portions 104 of the lining material are just located in the broken portion of the pipe line so that the overlapped lateral end portions which are weakly bonded by the aid of a thickened thermohardenable resin contained in the lining material are opened by the internally exerted fluid pressure. In this case, the inner tubular plastic film 105 also spreads out of the broken portion 102 of the pipe line, but this tubular film 105 is locally expanded seriously and finally ruptured by the fluid pressure to permit escape of the fluid. Even if the overlapped lateral portions 104 of the lining material 103 are not located in the broken portion 102 of the pipe line 101, the lining material 103 in the broken portion 102 is expanded while permitting separation of the lateral end portions of the lining material within the pipe line 101. The remaining tubular film 105 no longer functions as a reinforcing material for the pipe line 101.
Furthermore, it is noteworthy that the pipe line is sometimes surrounded by a high pressure underground water. If the pipe line has a broken portion, a large amount of water intrudes into the pipe line through the broken portion thereof so that the pipe line is flooded or at least submerged with water throughout. In case a lining material is applied onto the inner surface of such a pipe line, the lining material is externally wetted with water so that the lining material cannot be thermocured or at least needs a long period of time for curing, even if it is internally heated.
The FCM-sheet lining material disclosed in Ref. 1 is certainly superior in mechanical strength to the SMC lining material but the former is still unsatisfactory in mechanical properties for applying it onto pipe lines. The SMC sheet in FCM-sheet is poor in strength and elongation at the time of break-down while the fabric sheet in FCM-sheet is great in strength and elongation at the time of break-down. Thus, the SMC sheet is broken down by a weaker force as compared with the fabric sheet. In case of the FCM-sheet usually employed as a lining material and comprised of a SMC sheet of 4.0 mm in thickness and a fabric sheet of 0.3 mm in thickness, for example, these sheets showed the following properties: a strength at break-down of 43 kg/5 cm and an elongation at the time of break-down of 1.8% for the SMC sheet, and a strength at the time of break-down of 273 kg/5 cm and an elongation at the time of break-down of 24% for the fabric sheet. When tensile force is exerted on the SMC sheet, the force is concentrated of a relatively weak portion so as incur local elongation and break-down. On the other hand, the fabric sheet shows a great elongation at the initial stage of applying tensile force due to stretching of the relaxed yarns in the fabric structure, but its resistance to tensile force is rapidly increased after allowing the yarns to stretch to a certain degree. If the SMC sheet is integrally combined with the fabric sheet as in FCM-sheet, the force locally exerted to the SMC sheet is dispersed so that the strength and elongation at the time of break-down are somewhat improved. In case tensile force is increased beyond a certain limit, however, the SMC sheet alone in FCM-sheet is broken down. In the above example, the strength of the SMC sheet at the time of break-down was 57 kg/5 cm and its elongation was 2.4%. Accordingly, if a strong tensile force beyond a certain limit is exerted at the time of inserting the FCM-sheet lining material into pipe lines, the SMC sheet layer alone is broken, thus leading the lining treatment to failure. More specifically, the FCM-sheet lining material used for a conventional sewage pipe of 300 mm in diameter has a width of about 1000 mm and the strength of the SMC sheet layer thereof at the time of break-down is 1140 kg (57/50.times.1000). This apparently means that if a load of at least 1 ton is applied at the time of inserting the lining material into the pipe, there may be a possibility of the SMC sheet layer being broken down. In general, the load at the time of inserting a lining material into a pipe line depends on the length of the pipe line. Thus, a significant load is applied to a lining material in the event the lining material is long and the pipe line is also long. If the length of a pipe line exceeds 80 meters, the maximum load applied to a lining material being inserted into the pipe line will sometimes exceed 1 ton. Further, when the pipe line is seriously damaged or is irregular in size or is curved, the load will readily exceed 1 ton even if the length of the pipe line is far less than 80 meters.
In general, a sewage pipe line is constructed by connecting a great number of Hume concrete pipes in serial. If such Hume concrete pipes are broken locally, only damaged portions are repaired by replacing the damaged pipe with a new Hume concrete pipe. It is very common in this case that the pipe where the broken portion is formed is cut in two positions so as to remove only the broken portion and the pipes thus cut away are interconnected with a repair pipe which has an outer diameter equal to the inner diameter of the cut pipes. If such sewage pipe line has been repaired several times, therefore, the inner diameter of the pipe line varies according to the repaired positions. Accordingly, if the pipe line once repaired is again to be repaired, the second repair pipe becomes smaller in inner diameter than the first repair pipe. Thus, the pipe line is constructed as a whole by pipes with different diameters. If this pipe line is lined with a tubular lining material with a definite diameter, the lining material tends to form a wrinkle in the location of repair where the diameter of the pipe line is considerably smaller.
The lining material introduced into a pipe line is applied evenly onto the inner surface thereof by sending pressurized fluid, e.g. compressed air to the inside of the confined lining material. The lining material in this state is then internally heated to cure the thermohardenable resin to form a rigid fiber and/or fabric reinforced plastic inner pipe as a whole. A general and simple method for heating the lining material internally is to confine it, for example, with mouthpieces provided with an inlet and outlet and to introduce superheated steam into the lining material in confined state whereby the lining materially is heated internally under pressure. The curing of the thermohardenable resin is effected within a short period of time at a high temperature. In case of an unsaturated polyester, for example, curing of the resin proceeds rapidly by self-exothermic reaction. However, the outer surface of the lining material is contacted with the pipe line and the pipe line is in turn contacted with the surrounding ground so that much of heat supplied is lost. In order to heat the lining material sufficiently, therefore, the pressure of the superheated steam has to be elevated to about 3 kg/cm.sup.2 for heating the lining material at 100.degree. C. or higher. Care should be taken, however, that Hume concrete pipes usually used for sewage pipes are poor in pressure-resistance and tend to rupture under pressure of about 2 kg/cm.sup.2. This tendency is significant if the pipe line is superannuated. In a conventional method for heating the lining material, therefore, a high pressure steam cannot be used and a considerable period of time is needed for heating the lining material.
Under the above circumstances, a need arises for improving a means for applying a lining material to pipe lines having damaged portions, especially superannuated sewage pipe lines in a simple and economical manner and also a great demand for developing a new type lining material which can be inserted into a pipe line having damaged portions without difficulty and is capable of forming a rigid fiber-reinforced or fabric-fiber-reinforced plastic (FRP) lining on the inner surface of such pipe line.